Grinding and hindered settling classification of naturally occurring ores, etc. by density inducing constituents derived from the ore itself



APrll 20, 1954 P. G. KIHLSTEDT 2,675,966

GRINDING AND HINDERED SETTLING CLASSIFICATION OF NATURALLY OCCURRING ORES ETC., BY DENSITY INDUCING CONSTITUENTS DERIVED FROM THE ORE ITSELF Filed Feb. 27. 1948 2 SheetS-Sheet 1 Eg l j m ,2; j SCREENS 1 & m3 13/ v 1 t 4 amvauf /27 A A i /2/ 05 P5 GUDMAA Imus rznr BYXGZDM,M,MQM

Aprll 20. 1954 P. s. KIHLSTEDT 2,675

GRINDING AND HINDERED SETTLING CLASSIFICATION OF NATURALLY OCCURRING ORES ETC. BY DENSITY INDUCING CONSTITUENTS DERIVED FROM THE ORE ITSELF Filed Feb. 27, 1948 2 Sheets-Sheet 2 64w CPI/SHED DEE PEO wnuva ABNOEMAL m-ws/ry X .D/LV rave ware M/l L PZUV/D/NG IBIVOPMAL 0/: arm/v 3/ v 329 5/26 DI C'PIMINAT/NG CZASS/F/EB F'INE WL U55 7 Fl/BT'I/EE [560F587 TEEITMENT PER Gl/DMJP Alf/LSTEFT u-42M MMM Patented Apr. 20, 1954 SI I TION OE NATURALLY .R 1 omas, ETGI, BEL/DENSITY INDUCING o SIITUENTS DERIVED FKO 'T EWOR 1 PeficiGudmar. Kihlstedt, Nookeby, Stockholm,

Swedema s m to de sz'Gmvakfieh la s- Skefleftekamn, Sweden, 21; a limited, joint-stock Application-Eeb 'nary 27, 1948, Se1ialNo. 11, 821 7 Claims priority, application Sweglen. JnneYZIQE-lQQS" zcl ims z (Gian-:20

1-: invention..re1atesL to hindered settl iiig classification methodsof fflactionatiiig(naturally occurring mineralaggregates", Iori. "ores, "into one fraction containing. significantly 'val'uabl'e 'con' stituents of the; ore, and, intoanotlier fraction containing- ,significantlyfgangufe, V or. 'waste, constituen ts of' thio're. Hretbforathe fractionating, bath of; Suspended? ore'jparticles .has had its density controlled heiaddition thereto of some weightinglag'entlthat s'gext aneous or for'ignto theviore jan diii'hicli' accordingly} must be washed from, the recovered Q values before final. treatment Th'is'i vehtion, therefore, has as. one' of its main.featuresrthegcontrol of the increased density} oftlie; weight-fdisci'i'r'ninating hindered Settling classificatibrl bat j idl'lsityn-ihducii'lgf constituentsderivegi fromftli or'eit'selfl Thin'vention ,pfonoses' itliepfetieatinent of the ore. during' its lbirieficialtiohjby subj eating. it, prior to itsi being.groundg-in the, usual closed. circuit grinding .stationl toIgiravitm-ihdiiced fractionation along, hindered-Settling classification 1i'nes',.'jso' thatLone'L. fraction cor'itains relatively light Sig-.- nifi'antly gangfi'oonstitueiitsf of the ore and an -v othrjract'iori contains lrelativelyrlheavy signifi; cantly' metallic; va ues of the ore] that 3 may "lie fuftfir itiieatedTozfl their" recovery. 'A featureof fnoyelty. of theflfirifi'h'tibh reside in controlling" the ilcreased'iden's'ity, VofftHe"weig I-di'sciiiinifiat; mg, hindered-settlingjclagsification atl'fby sup; plying thereto" gravityelhducifigconstituents of the, raw ore itself drawn from anyisuit'abl'e point of the usual; close .oifc'uiti grinding station including'fa ysine-discriminating classifier niwmcn the, ore Values are being classified predominantly into; 'sizef groups.

Values, 'fractionated out. from the crushed .raw ore by j' the wight disc'liminatifig" bathfwhicli have been substantially jfr'ediof 'gahgtiebo'nstit uentjs by" passing, ft'hroughf that hath. are then supplied tothe usual 'closed circuit grinding station'," from which st'at ion thei bene'ficiated ore values ,emer'ge{"'after treatment in a pre'djomi nantly"size dicriniinating or classifying ham so that theyaie of a; particle size small "enough'jto unlock" or expose the 'valiies" to faxfilitatei the usual subsequent; values-recovery treatment Steps? v M v t v .i

A usna-lclosed circuit;grinding'station(comprises" a fine-grinding; mill that discharges" nto an? agitating classifier "having" a sloping 1 bottom or deck" adaptedfto pom;- a -'predominantly, size discriminafiing b of the ore" particle' "in suspension; Agita g rakes rake- 'the'- settledflarger 1 5 coafse sized panic ee' us ailyca nq "Sands;

valfi'e' nan'y given-ease correspondingto=-tna ro a solids content of approximately 40% by vdliifmi v'iwi h 9 Q1 s ei n ores in which there is a substantial difierence between the specific gravity of the desired mineral and that of the unwanted gangue, but more particularly to massive sulphide ores and to iron ores where the heavy mineral comprises a substantial proportion of the total weight. The improved method is especially applicable to such massive ores where the heavy minerals have a higher grinding resistance than the gangue and thereby cause an accumulation of such a pulp in the closed circuit which is enriched in heavy minerals. The method is also applicable to coal cleaning and to so-called non-metallic ores carrying a relatively heavy mineral such as fluorspar.

Another feature of this invention relates to the manner of controlling the density of the bath in the size-discriminating classifier (namely, its dilution) thereby determining the particle size above which particles settle and emerge as rake product or sands, and below which the fines pass as overflow. In other words, the line of size division between the two fractions is determined by the dilution of the bath of that classifier. The more dilute the bath the smaller or finer will :be the particles of the overflowing fraction, and conversely. The diluting water supplied to that bath, in a closely controllable manner, comprises the water used to flow through the screen or screens that make screened fractions of the overflow (principally gangue material) from the weightdiscriminating classifier. Thus, the bath in the weight-discriminating classifier is controllably rendered sufficiently dense while the bath in the size-discriminating classifier is controllably rendered sufficiently diluteboth by the use of constituents present in the cyclic system and not involving the addition of constituents extraneous or foreign to the ore. The said dilution in the size-discriminating classifier gives a high content of heavy finer particle values in the intermediates bled off from the bath of that classifier to be supplied as weighting agents to the bath in the weight-discriminating classifier.

By way of a more detailed explanation of these and other features of my invention, referenceis made to the following description taken in conjunction with the accompanying drawings in which:

Figures 1, 2 and 3 are diagrammatic flow sheets I of ore concentration plants according to the present invention. In these diagrams three-digit reference numerals are employed for convenience, the first digit indicating the figur number while the last two digits, when identical in the several figures, serve to designate functionally equivalent apparatus elements.

Referring to Figure 1, raw crushed ore is introduced into a weight-discriminating classifier IOI where the lighter gangue constituents are separated and overflow via line I II while the heavier, and valuable, ore values are removed by means of the rake of the classifier and discharged through line I23. The values leaving via line I23 are introduced into th grinding system of the ore dressing arrangement, which grinding. system includes the fine grinding mill I03 and the sizediscriminating classifier I05, which may be for example, of the hydro separator type. 1 The values introduced via line I23 are mixed with the larger sized particles removed from the size-discriminating classifier I05 via line I27 and are introduced into the mill I03, where the particles are suitably reduced in size.

'Eflluent from the grinding mill I03 is introing mill for further treatment in the grinding circuit.

A portion of the eflluent from the mill I03 is introduced via line I3I into the bath of the weight-discriminating classifier IOI, where this portion functions as the gravity-inducing constituent imparting the desired density to the bath in order to permit the desired separation of the raw crushed ore in the classifier IOI on the basis of weight or density to take place.

Returning to the gangue which is removed from the weight-discriminating classifier IOI via line II I, this gangue material together with the pulp introduced into the classifier via line I3I and most of the fines possibly present in the new crushed ore supplied, is introduced into one or a plurality of screens H3 and H4 where it is subjected to washing with water (from a source not shown), the final gangue after washing being withdrawn through line H5 and rejected. In order to provide the proper dilution of the bath in the size-discriminating classifier I05, all or a portion of the wash water from screen II3 may be introduced via line I2I into the grinding system together with substantially all the returning pulp and said fines. More particularly, in the embodiment shown this pulp with wash water may b admixed with the material passing via line I25 from grinding mill I03 to the size-discriminating classsifier I05.

Meanwhile, and in order to maintain proper density in the bath of the weight-discriminating classifier IOI, the gravity-inducing constituents therefor are introduced via line I3I in the form of a suspension in all or a portion of the wash water resulting from the second screening operation. For example the wash water from the washing of the gangue on scr en II4 may be introduced via line MI into the grinding system at a point just ahead of the place from which the gravity-inducing substituents are withdrawn via line I3I for introduction into the :bath of the weight-discriminating classifier IOI. As in the case of the first screen I I 3, the second screen I I4 is supplied with Water from a source not shown.

It will thus be observed that in this ore dressing system the wash water (together with pulp) from one or both of the screens II3 and H4 is used in such manner as to make it possible readily to control the density of the gravity-inducing constituents introduced into the weight-discriminating classifier I0 I Furthermore, the introduction into the closed grinding circuit of a portion of the wash water (together with pulp) via line I2I makes it possible readily to control the dilution in the size-discriminating classifier I05, which dilution in turn permits an excellent control over the particle size of the fine values of the ore removed via line I29 to further recovery treatment .(not shown).

' Figure 2 shows another modification of an ore dressing system which closely resembles that of Figure l and in which corresponding reference numerals have been employed, with the exception that here the reference numerals are of the 9200 series rather than the series as in Figure 1. The essential difference between the system of Figure 2 and that of Figure 1 is that in the former a separate classifier '25I is inserted in aiming-acc the elosed g'rlndfi1g system in order to provide =a preliminary separationof thecoarser of the particles resulting frorrfi-the grinding operation; in

grinding-"mill-'20 3 'and th'ereby to providea-more stable" suspension for the weight di's'c'riminating ground partic-les withdrawn fi-'om'=-mill 203}- materials thatpa'ss-through-the mill 2ll3 without heii i-greduced to a suitably fine size to beremoved prior to introd'i'icticmthereof into the 1 "sizediSeriI-ninating -CMSSifir- ZUSJ a It? will be observed that the suspensioniof materialstleavingigrmding mill 20'3- is; introduced via line 225aainto theabath ofalth'e iclassifiers25il The relativelycoarser particlesvseparatedinthis classifier are returned via linee253 to'the mill 2033 togetheriwithiemergedisands otheavierparticles: fromithe weightediscriminating..classifier='2 l that arei'zfed-s to 2..theefgrindingissystem via:. linece' 223; Einailly l-the relatively coa'rseriparticles :from; the siZea-e1iscriminatingi-v classifier: 205-: are: also: re-. turned twthesmillil fl 3 .v'i a line'22'i1to complete the circuit ofzsmateria-lsxiriithezgrinding system; The. relatiwelye fineeparticlesthat. .are, a. separated in; classifier: Zileoverflowe therefrom and: are intro! ducediviazilina ifib into:theesize-discriminating,

claissifierelfiiil I l I orderx tmadjustz to thezdesiredivalue10f the densititpf theabathfinithe-sweightediscriminating classifierfi. 011;. aiportionzcor'res-ponding to. said de: sired value of theloathcontaining gravity-induce ingaconstituentst-isaremovediirom the classifier 25 i "randeintroducedsyiajineai! 321'; into-:the; bath .of. the weightediscriminating:classifier 201 Ivprefer. to: eremovei this: portionwfrom .a.-=.-point ."below; and spacedifrom theilevel ofithe bathsin-the classifier.

The relatively light :gang-ue materialoverfiowe 'inglfrom therweightediscriminating:,classifier' 2M and-removed: via -line=-2 I is. washed: on screens 2L3 and; 2H withwaterfrom a source notshownz: All. or=:a portion; of; the wash water from: screen* 2l 3 -iseintroducedi together with pulp into the classifier.2-5lvia;.line22-2l thus enabling the desired 'tdilutionrm .the-size discriminating classifier 2ll5 ultimatelyi to: be olotained; Also additional amountssof-iwash water from the secondscreen 2 ld-may-beintroduced.into' the bath of the classifier; 25 l -via=line 2M. The-vwashedgangue materialis withdrawn from the screens via line 2 l 5 and rrejected;

According to Figure-3, the ore treating system includes a. weightediscriminatingclassifier 30I which may, 'for-examplebe ofthe rrake type, a suitable.-.grinding }mill i303], which may -beof the ball mill type; and a sizeediscriminating classifier 305, .which mayalsobeo'fthe-rake type.- Receiv-- ingnthe. overflow vfrom: the weight discriminating classifier! yia line 311 isa screen 3l3-that providesiscreened (and washed) fractions of. the overflow fromathe. weightediscriminating classi fier "301. The .worthless, or relatively worthless, gangue'. .obtained as .a llresult'i. of; the "screeningv operationis rejected [viavline .315. Line. 3 I 1" 'pro-' vide'dswitheaisuitable valve 319' serves-to intro duce 'wash waterto assist in the screening" and" .of the amount-'ofpulp supplied and of the con=-- sistemt'y "of the mill materials are-equalized; as well as further- ;Jer-mittin'g-- any undulycoarse washing operatiomapplied tzrthe-gangueederiyediz from the overflow from the weighti-discrimmat ma classifier 3M. :5 Thai wash zwater :from this screeningoperation;whichris employed for:di1u-: tion purposes asidescribed' more:fullyrhereinatter; may: b e introduced-'- together withitheapulp return! ing from theclas'sifier flllt via dine- 32 l te =the..-size==- discriminating-classifieri3 fl5t ReturniIi-g tirthe weight discriminating.lclassi fier 30-1? the emerged? sands or heavy 'particlesa: separated thereby: are: introduced via line 3 2 3 tot grinding mill 30' 3 where theyeare"suitably reducedin=size'..-'- The grou-ndparticles leaving thismill are then introduced' via-line= 3z5 into lth'e bath of the size-discriminatingclassifierfi05 wherein separa tion of the ore: values predominantly into: :size group's-take$ place$- The emerged sands: or coarsaparticles frornithe size-discrimmating'-'c1assifier 305 are recyele'cl. to mill "3o3 viaziline' 32lg wliile at the same time-the fines-are removed a's-overflowsvia-li-ne 329;- These fines "may then betaken to' a further recovery: treatment which forms nopart -ofthe pres'erlt' Returning to 'a consideration of the-operation of-the size-discriminatingclassifier-305a suspen=-= sio'n of -the h'eavy values bearirig- -ore particlesundergoing classification predominantly into' si'zegroups "is 3 withdrawn: fromthe *bath therein via line 33 I provided with a suitabl valve-*3 33, and is introduced-into the b'ath in' thepretreatment station; namely; the bath con--tained-- in; the weight discriminating classifier '3 (H By =a suit-' able adjustment of-valve '333, either-alone or in conjunction with a suitable adj ustm'ent' of the rateef introductionofwash water which is intro olucecl togetherwitlrpulp into the bath'oft'he size discriminating classifier 305 via line 32!, the de sired 'density 'or specific-'grav-ityof the bathin the weight discriminatihg classifier:'- 3 01 is obtaine'd.

Summarizingthe operatiorraccordingto Figure 3, the" raw crus'hed 'ore undergoin'g treatme'n't isintroduced intothe weight discriminating classi fier 3M; where' -the coarse particles are-"ser iarated into light gangueparticle'sand lieavy values par-- ticles} 'Ilie'iformenpass over together with-fine particlespossibly ocurring theraw crushed oresupplied andwitlfipiilp law-the overflow-Via line 31 whizl the la tt'er 'pass-wia -lin 323 to mill 3G3 whereth'ey are' su-itabl-y reduced ih size-and then introduced inwthe--"-size discrimina tin classifier "305. T1 ie -gangue particles" are then' washed -on scre'en' 3l3' whileadding -sufficienv diluting= weaves-w ived ime -311 to provide a wash water,whieh; when'introdiiced into th'ebath of the -size-'-=di'scriminating classifier"'"305 *viarline' 32-! will provide-the desired-dilution of the latter bath in order toefie'etthe separation of the'heavyore values into"fine-particles of the" desired size" which "pass -over into the-overflow" via line 32 9, whilef'permitting the"coarsefparticlesto be' 're moved as rake product" and-recycledvia' line" 32! to themi1'1"3l1l3" l In the meantime a portion of tli'ej'b'ath' in' the sizeedi's'eriminfating c'lassifiefi305. isremoved and cycled yia yalveddine 331) to 'theiweight-fdiserimi-f natingj classifier 301.1 Bye suitable adjustment" of the dilution obtained by, means ofithe wash: Water introducedvia line 3ZI'fas'We11'a's the rate of cyclingfof material throughjlirie 331, the bath in' the wweightdiscriininatingclassifiiaritlll is'adjustedto the de'sir'ed-fdensityto efiect the desired preliminary. separation 'of' light, 'ganguei from heavy fore values;' jall' without; the introduction of any extraneous or foreign 'materialinto any part of the system-other of course than diluting water via line 3 II.

By way of summary, it will be observed that the three ore dressing systems that have been described are characterized by the common feature that they permit the ore dressing operations to take place without requiring the addition into the system of weighting or separating agents that are extraneous or foreign to the ore and which ultimately must be removed from the beneficiated ore before final treatment. Thus the weight-discriminating classifiers NH, and of Figures 1, 2 and 3, respectively, are supplied with a suspension of gravity-inducing constituents that are derived from the ore itself introduced to the respective classifiers via lines I 3 l, 23| and 33!, respectively. Furthermore, the desired dilution in the size-discriminating classifiers I05, 205 and 305 is brought about by the introduction of. wash water obtained during the washing operation and performed upon the gangue material that overflows from the weight-discriminating classifiers it'll, 20! and 33!, respectively, this wash water being introduced in part at least into the baths of the size-discriminating classifiers via lines I21, 22! and 32 l, respectively. Moreover, the ore dressing system shown in Figure 3 illustrates more specifically additional features of control whereby a suitable adjustment of the valve 3!!! in the line 311 to which the diluting water for washing the gangue is introduced into the system, either alone or in conjunction with a suitable adjustment of the valve 333 in the line 33l through which is cycled the gravity-inducing constituents to the bath of the weight-discriminating classifier, provides very close control over all parts of the ore dressing system. It will be appreciated of course that the optimum rates of supply of wash water to the system and of return of density-inducing constituents from the bath of the size-discriminating classifier to the bath of the weight-discriminating classifier will depend in any given instance upon the nature of the particular ore that is, undergoing treatment. Those skilled in the art will be readily enabled to arrive at these optimum values in any such given instance with the aidof the description of the invention set forth herein.

When treating some massive ores, material from the coarse ore separated from gangue in the weight-discriminating classifier NH, 20! or 301 respectively (Fig. 1, 2 or 3 respectively), in line I23, 223 or 323 respectively may be removed as a finished product as shown in the drawings with the dashed lines l23a, 22311 or 323a respectively. In this case said material is not supplied to the grinding mill and the closed circuit grinding system will only work with the fine part of the raw crushed ore which has overfiowed from the weight-discriminating classifier IOI, Zill or 30 l respectively and, via line HI, 2 or 3 respectively and line I2], 22! and 32! respectively, past the screens and been introduced into the closed circuit grinding system. In this case the raw crushed ore is divided into one coarse finished ore, one rejected gangue and one intermediate part which after grinding in the mill I03, 203 or 303'respectively is removed for further recovery treatment via lines I29, 229 or 329 respectively.

This application is a continuation-in-part of my copending application Serial No. 676,220, filed June 12, 1946, now abandoned.

While various specific examples of preferred methods embodying the present invention have been described-above, it will be apparent that many changes and modifications may be made in the procedure herein described without departing from the spirit of the invention. It is therefore to be understood that the particular procedures set forth above are intended to be illustrative only and are not intended to limit the scope of the invention as defined in the following claims.

Iclaim:

1. The process of beneficiating ores by separating them into fractions respectively richer in valuable and in waste constituents of the ore, which comprises supplying the raw crushed ore to a bath containing a dense suspension flowing through the bath, the density of the suspension and its rate of flow being controlled to maintain the density intermediate the densities of the constituents of the ore; removing from said bath a lighter fraction of the ore as finished product; supplying to a closed circuit grinding system the more dense fraction of the ore, said closed circuit grinding system including a grinding zone and a classification zone having predominantly size-discriminating capabilities for yielding one fraction of an overflowed suspension of finer solids and another fraction enriched in larger and heavier solids; recycling said fraction of larger solids to said grinding zone and recovering the fraction of finer solids for further treatment; and recycling to said bath containing the dense suspension a portion of the finer material circulating from the classification zone of the closed circuit grinding system and containing as predominant constituents the said finer enriched fraction, the aforesaid dense suspension fiowing through the said bath containing the dense suspension for separating by gravity the coarse material of the ore initially supplied into two fractions of substantially difierent specific gravities, the density-inducing constituents of the said dense suspension being derived exclusively from the ore undergoing treatment; the lighter fraction from the bath containing said dense suspension being subjected to screening, and the resulting finer ore particlesbeing supplied to the bath of said classification zone having predominantly size-discriminating capabilities.

2. The process of beneficiating ores by separating them into fractions respectively richer in valuable and in waste constituents of the ore, which comprises supplying the raw crushed ore toa bath containing a dense suspension flowing through the bath, the density of the suspension and its rate of flow being controlled to maintain the density intermediate the densities of the constituents of the ore; removing from said bath a lighter fraction of the ore as finished product; supplying to a closed circuit grinding system the more dense fraction of theore, said closed circuit grinding system including a grinding zone and a classification zone having predominantly size-discriminating capabilities for yielding one fraction of an overfiowed suspension of finer solids and another fraction enriched in larger and heavier solids; recycling said fraction of larger solids to said grinding zone and recovering the fraction of finer solids for further treatment; and recycling to said bath containing the dense suspension a portion of the finer material circulating from the classification zone of the closed circuit grinding system and containing as predominant constituents the said finer enriched fraction, the aforesaid dense suspension flowing through the said bath containing the dense suspension for separating by gravity the coarse material of the ore initially supplied into two fractions of substantially different specific gravities, the density-inducing constituents of the said dense suspension being derived exclusively from the ore undergoing treatment; the bath of the size-discriminating classification zone being supplied with wash water derived by washing the lighter fraction'of the waste constituents at a rate such as to dilute said bath to a value such as to effectvseparation as between fine and coarse ore values having a predetermined size.

Number Number Name Date Wuensch Jan. 31, 1933 Wuensch Dec. 31, 1938 FOREIGN PATENTS Country Date Great Britain June 8, 1938 Germany July 17, 1940 

